What is Block Lava Flow?
Block lava flow, also known as ‘A’ā flow, is a type of lava flow that is characterized by its unique texture and formation process. In this article, we will explore the definition, composition, and characteristics of block lava flow, as well as its differences from other types of lava flows.
Definition and Composition
Block lava flow is a type of lava flow that consists of large, angular blocks of lava that are stacked on top of each other. These blocks are formed when the lava is partially solidified and then torn apart by the flow’s movement. The composition of block lava flow is typically andesitic or basaltic, with a silica content ranging from 55% to 65%. This higher silica content gives block lava flow its characteristic black or dark brown color.
Formation Process
Block lava flow is formed when the magma reaches the Earth’s surface and begins to flow. As the lava flows, it cools and solidifies, forming a crust. The crust is then torn apart by the movement of the lava beneath, resulting in the formation of blocks. These blocks are often smooth on one side, known as the pillow lava, and rough on the other side, known as the ‘a’ā.
Characteristics
Block lava flow has several distinct characteristics that set it apart from other types of lava flows. Some of these characteristics include:
- Size: Block lava flow is characterized by its large size, with blocks ranging in size from a few inches to several feet in diameter.
- Shape: The blocks are typically irregular in shape, with a rounded or angular shape.
- Texture: The blocks are smooth on one side, known as the pillow lava, and rough on the other side, known as the ‘a’ā.
- Color: Block lava flow is typically black or dark brown due to its high silica content.
- Composition: Block lava flow is andesitic or basaltic in composition, with a silica content ranging from 55% to 65%.
Differences from Other Lava Flows
Block lava flow is different from other types of lava flows in several ways. Some of the key differences include:
- Pahoehoe lava flow: Pahoehoe lava flow is characterized by its smooth, billowy surface, unlike the rough, blocky surface of block lava flow.
- Pāhoehoe lava flow: Pāhoehoe lava flow is a type of lava flow that is characterized by its rough, chunky surface. It is different from block lava flow in that it is formed by the slow cooling of the lava rather than the tearing apart of the crust.
- Ultramafic lava flow: Ultramafic lava flow is a type of lava flow that is characterized by its high magnesium content and resulting dark color. It is different from block lava flow in that it is more fluid and has a smooth, glassy surface.
Table: Comparison of Lava Flows
| Block Lava Flow | Pahoehoe Lava Flow | Pāhoehoe Lava Flow | Ultramafic Lava Flow | |
|---|---|---|---|---|
| Size | Large, angular blocks | Smooth, billowy surface | Rough, chunky surface | Fluid, smooth surface |
| Shape | Irregular | Irregular | Irregular | Smooth |
| Texture | Smooth on one side, rough on the other | Smooth | Rough | Smooth |
| Color | Black or dark brown | Yellow or orange | Red or orange | Dark gray or black |
| Composition | Andesitic or basaltic | Basaltic | Basaltic | Ultramafic |
Conclusion
Block lava flow is a type of lava flow that is characterized by its unique texture and formation process. Its composition is typically andesitic or basaltic, with a silica content ranging from 55% to 65%. The blocks are formed when the lava is partially solidified and then torn apart by the flow’s movement, resulting in a rough, blocky surface. Understanding the characteristics and differences between block lava flow and other types of lava flows can help us better appreciate the unique features of each.